Optical arrangement for a passive infrared motion detector

Abstract

An optical arrangement for a passive infrared motion detector which has an infrared detector unit and a system for directing infrared radiation from at least two separate directions to be monitored onto the detector unit characterized by the system including a single focusing device and separate, flat reflecting surfaces or directing mirrors, which are arranged with at least one flat reflecting surface associated with each direction to be monitored to reflect a beam or solid angle of radiation from the direction onto the single focusing device which device will focus the radiation along a folded beam path to the detector unit.

We claim: 
     
       1. In a passive infrared motion detector having an infrared detector unit and means for directing infrared radiation from at least two separate directions to be monitored on said detector unit, the improvements comprising the means for directing including a single means for focusing radiation from more than two directions simultaneously and more than two separate, flat reflecting surfaces, said single means for focusing radiation including a single concave mirror having an optical axis and a deflecting mirror being arranged on the optical axis of the concave mirror and at an angle therein to deflect light focused by the concave mirror at an approximately a right angle to the optical axis and onto the infrared detector unit so that the focused radiation from said concave mirror travels to the detector unit in a folded path with two portions extending substantial at right angles to each other, said flat reflecting surfaces being a plurality of individual separate flat reflecting surfaces with at least one being arranged on each side of the optical axis of the concave mirror, said reflecting surfaces being arranged with at least one reflecting surface associated with each direction to be monitored to reflect the radiation simultaneously from said direction onto said concave mirror with at least two of the reflecting surfaces having planes extending at different angles to the optical axis. 
     
     
       2. In a passive infrared motion detector according to claim 1, wherein each of the flat reflecting surfaces is an individual separate, flat director mirror, said director mirrors being arranged in a louver-like pattern for reflecting beams from different directions at portions of the concave mirror. 
     
     
       3. In a passive infrared motion detector according to claim 2, wherein the director mirrors are adjustably mounted to enable changing the directing of the beams being directed onto the concave mirror. 
     
     
       4. In a passive infrared motion detector according to claim 2, wherein each of the flat director mirrors has a longitudinal axis extending parallel with each other and perpendicular to the optical axis of the concave mirror. 
     
     
       5. In a passive infrared motion detector according to claim 4, wherein each of the flat director mirrors is positioned between the space being monitored and the detector unit, and each of the mirrors is separated from adjacent mirrors by openings having equal areas with a longitudinal axis extending perpendicular with reference to the optical axis of the concave mirror. 
     
     
       6. In a passive infrared motion detector according to claim 5, wherein each of the flat director mirrors are adjustably mounted to rotate on their longitudinal axes. 
     
     
       7. In a passsive infrared motion detector according to claim 1, wherein the plurality of flat reflecting surfaces are provided on a member as flat mirror facets with a facet associated with each one of the directions being monitored. 
     
     
       8. In a passive infrared motion detector according to claim 7, wherein the deflecting mirror of the means for focusing radiation is arranged between the flat reflecting surfaces and the concave mirror.